The present invention relates to a position detection device, and more particularly to a position detection device in which a two-dimensional light receiving means has a function of an electronic shutter for discharging an accumulated electric charge in order to adjust the quantity of received light, and light is emitted within a period of time during which the electronic shutter is stopped and the two-dimensional light receiving means is accumulating an electric charge.
There is a position detection device that detects a position of a target by emitting light toward the target to receive reflected light. This position detection device is, for example, a tracking device such as a surveying instrument that measures a target position. In this case, the target position is indirectly shown by a prism that reflects tracking light coming from the tracking device such as a surveying instrument.
In addition, the tracking light, which has been emitted by the tracking device such as a surveying instrument, is reflected by a prism located at the target position so that the reflected light is received by a light receiving element mounted on the tracking device. This light receiving element is constituted of a light receiving sensor, and an light receiving optical system for sending reflected light to the light receiving sensor. By imaging received light at a specific position of the light receiving sensor, it is possible to detect and judge whether or not collimation of the tracking device agrees with the target.
There is a four-division sensor as a typical light receiving sensor. This is a sensor whose light receiving area is divided into four with respect to a center of the light receiving sensor. The central position can be detected by comparing the quantity of received light among four areas. A collimation direction of the tracking device is controlled according to this output signal. However, if the collimation direction deviates from the center and thereby light is received in one area, what is found out is only existence of the center in the area.
For example, a tracking device, which uses a four-division sensor, has been developed. This tracking device comprises an amplifier that differentially amplifies outputs of a pair of division elements facing each other in a horizontal direction of a four-division light receiving element, and outputs of a pair of division elements facing each other in a vertical direction, respectively; and a horizontal-direction integrating circuit and a vertical-direction integrating circuit that level an output signal in a horizontal direction, and an output signal in a vertical direction, which have been output from this amplifier, respectively. Tracking is performed by controlling a motor according to the control signals.
In addition, although it is more expensive than the four-division sensor, there is an area sensor that can detect a position at which light is received. This area sensor is constituted of sensor parts that are finely divided in two-dimensional manner. If an object is in a sensor area, this area sensor can detect its position. This sensor is capable of collimation control with a higher degree of accuracy than the four-division sensor. For example, a tracking device, which uses an area sensor, has being developed. A surface of this area sensor is divided into small surface elements so that an incident position of light can be identified in a two-dimensional manner. Tracking becomes possible by controlling and driving a vertical-direction driving device and a horizontal-direction driving device using an arithmetic processing means so that incident light comes into the center of the area sensor.
The four-division sensor and the area sensor as described above are sensors that receive reflected light. Because of it, a tracking range is equivalent to a range within which reflected light can be received. In order to increase the tracking range, it is necessary to increase intensity of emitted tracking light. However, an output limit of the intensity of emitted light is stipulated so that human eyes are not damaged. Therefore, the intensity of emitted light cannot be increased without limitation.
Therefore, efforts to adopt a technology for extending a tracking distance by using pulse light, and a technology for removing noise light by digitizing light receiving data and accumulating the data, are exerted. Nevertheless, because of the output limit of emitted light, there was a problem that a tracking distance cannot be extended dramatically.
A position detection device according to the present invention is devised to perform the following: a light sending means sends out emitted light, which comes from a light emitting means, to a target object; a two-dimensional light receiving means receives reflected light coming from the target object, and converts the reflected light into an electric charge; and an arithmetic processing means determines a position of the target object on the basis of a light receiving signal from the two-dimensional light receiving means. In addition, the two-dimensional light receiving means has a function of an electronic shutter for discharging an accumulated electric charge in order to adjust the quantity of received light. Moreover, the arithmetic processing means can drive the light emitting means within a period of time during which the electronic shutter is stopped and the two-dimensional light receiving means is accumulating an electric charge.